docs: def get_cache_mode(service, pool_name):
      """
      Find the current caching mode of the pool_name given.
      :param service: six.string_types. The Ceph user name to run the command under
      :param pool_name: six.string_types
      :return: int or None
      """
      validator(value=service, valid_type=six.string_types)
      validator(value=pool_name, valid_type=six.string_types)
      out = check_output(['ceph', '--id', service,
                          'osd', 'dump', '--format=json'])
      if six.PY3:
          out = out.decode('UTF-8')
      try:
          osd_json = json.loads(out)
          for pool in osd_json['pools']:
              if pool['pool_name'] == pool_name:
                  return pool['cache_mode']
          return None
      except ValueError:
          raise